Technical Field
Apparatuses and methods consistent with the exemplary embodiments relate to a light source driving apparatus, a display apparatus and a driving method thereof. More particularly, the exemplary embodiments relate to a light source driving apparatus, a display apparatus and a driving method thereof, in which a snubber is provided for preventing voltage and current spikes generated in switching of a switching device.
Description of the Related Art
In a display apparatus such as a television (TV), a driver for driving a light emitting diode (LED), or the like, light source may include a driving circuit to which a tapped-induced boost converter (hereinafter, referred to as a ‘TIBC’) method is applied.
FIG. 1 is a circuit diagram showing a TIBC driving circuit of the related art, and FIG. 2 shows ideal waveforms of the TIBC driving circuit of FIG. 1.
The waveforms shown in FIG. 2 are ideal waveforms in which all parasitical components of the circuit are ignored, without reflecting noise generated in implementing the practical circuit. For example, N1 and N2 of FIG. 1 indicate magnetically coupled inductors serving as a transformer. In FIG. 1, a leakage inductance component L1k inevitably parasitic on the transformer is not shown, and a capacitance component Cds between a drain and a source parasitic on metal oxide field effect transistor (MOSFET) M1 is not shown.
In a boost converter of the related art, voltage stress applied between both ends of the MOSFET is equal to Vo. However, in the TIBC, as shown in the waveforms of VD of FIG. 2, voltage stress applied between both ends of the MOSFET is drastically lowered into (N1Vo+N2Vi)/(N1+N2), but an advantage of lowering the voltage stress is cancelled out by the leakage inductance L1k and capacitance Cds.
FIG. 3 is a circuit diagram showing a TIBC driving circuit including a main parasitical component, and FIG. 4 shows waveforms of the TIBC driving circuit of FIG. 3. The waveforms of FIG. 4 show real waveforms of the TIBC circuit in FIG. 1, which involves waveform ringing due to parasitic components as compared with the ideal waveforms of FIG. 2.
Specifically, as compared with the waveforms of FIG. 2, the waveforms of FIG. 4 show that a very high voltage spike and ringing due to the spike are generated in response to the MOSFET M1 being turned off (t—off), and thus the spike and ringing are generated in a current ip and id. The spike and the ringing are caused by resonance between the parasitic components L1k and Cds. As shown in FIG. 3, a drain of M1 is not clamped anywhere and connected to a tap portion to which primary and secondary winding wires are connected, and therefore VD increases without limit while energy stored in L1k is transferred to Cds by resonance. That is, if a current flowing in L1k just before turning off M1 is Ip, the spike of VD has an amplitude of Ip*√(L1k/Cds). Therefore, the voltage spike becomes higher as Ip increases, as L1k increases or as Cds decreases. For example, the spike having a high voltage of about 150-200V is generated when VD is about 30V.
As a method of preventing the spike and the ringing, the circuit may be changed to achieve voltage clamping, or to additionally include a resistor R, a capacitor C and a diode D that constitute an RCD snubber circuit. FIG. 5 is a circuit diagram showing an example where an RCD snubber 51 is applied to the TIBC circuit of FIG. 3.
However, the RCD snubber shown in FIG. 5, which is a dissipative snubber or a lossy snubber, is difficult to be applied to the TIBC circuit of the driver since it has disadvantages that an efficiency of the circuit is low and a snubber resistor generates a lot of heat.